Polynomial expansion of basis sets: Alternatives to fully optimized exponents

Alternatives based on polynomial expansions of gaussian basis set exponents are introduced and evaluated. The formulas presented here outperform methods based upon the even-tempered formula or combinations of it. They closely match the performance of other methods based upon larger polynomial expansions of the logarithm of the exponents using the same or one less parameter per orbital angular symmetry.     

Exact Gaussian expansions of Slater-type atomic orbitals

Three exact Slater-type function (STO) integral transforms are presented. The STO-NG basis set can then be developed using either only 1s Gaussian functions, the same Gaussian exponents for each shell, or using the first Gaussian of each symmetry. The use of any of these three alternatives depends only on appropriate numerical integration techniques.     

Supermassive Black Holes May Be Limited by the Holographic Bound

Supermassive Black Holes are the most entropic objects found in the universe. The Holographic Bound (HB) to the entropy is used to constrain their formation time with initial masses 10^6–8 M , as inferred from observations. We find that the entropy considerations are more limiting than causality for this direct formation. Later we analyze the possibility of SMBHs growing from seed black holes. The growth of the initial mass is studied in the case of accretion of pure radiation and quintessence fields, and we find that there is a class of models that may allow this metamorphosis. Our analysis generalizes recent work for some models of quintessence capable of producing a substantial growth in a short time, while simultaneously obeying the causal and Holographic Bound limits.     

Dihydroquinoline derivative as a potential anticancer agent: synthesis,crystal structure,and molecular modeling studies

Molecular Diversity - Cancer is one of the leading causes of death worldwide and requires intense and growing research investments from the public and private sectors. This is expected to lead to...     

Evaluations of the BET, I-point, and α-plot procedures for the routine determination of external specific surface areas of highly dispersed and porous silicas

Nitrogen adsorption isotherms of silicas and other oxidic materials are distorted by the presence of micropore adsorption and capillary condensation. This distortion affects the determination of the specific area of the material, depending on the chosen calculation procedure. Correction of the initial (total) isotherm for micropore capacity decreases or eliminates this source of error to give a useful estimate of the external surface area. In the present work, 26 silica-based adsorbent materials were studied to obtain total and external specific surface areas by the Brunauer-Emmett-Teller (BET), I-point, and α-plot procedures, using the micropore capacities from the α-plots to obtain the corrected (external) isotherms. Errors in the specific surface areas due to the presence of micropores are given by the equation ΔsA = 3.267 (m(2)/cm(3) STP) sV(mic), where sA is the specific surface area in m(2)/g and sV(mic) is the micropore capacity in cm(3) STP/g. A consistent set of conversion factors was obtained by which the external specific surface area obtained using one of these procedures can be converted, with part-per-thousand precision, to either of the others. Although the I-point procedure presents the advantage of not requiring a defined p/p(0) range, the α-plot procedure is recommended for routine determinations of external specific areas of silicas and other oxidic materials, except for cases in which the shapes of the adsorption isotherms of the sample and the reference differ significantly from one another in the p/p(0) range used for the determination.     

An investigation of chlorophenol proton affinities and their influence on the biological activity of microorganisms

The proton affinities of 15 chlorophenols are calculated by ab initio methods. Straight correlation between proton affinities and changes in the electronic structure is observed. The proton affinities decrease linearly with the electronic density gain on the chlorine atoms, as the liberation of the proton increases. To confirm the importance of the proton affinities on the toxicity of chlorophenols, calorimetric responses of these molecules and related ones where the acid proton is changed to a methyl group (anisol and its chlorinated derivatives) were used to verify their effects on Chromobacterium violaceum. The results confirmed that the chlorophenols are more toxic than the respective chloroanisols and suggest that high proton affinities are associated with low toxic activity. The toxicity of the chlorophenols can be associated with the respiratory mechanism in some microorganisms.     

A theoretical and spectroscopic study of conformational structures of piroxicam

Piroxicam (PRX) has been widely studied in an attempt to elucidate the causes and mechanisms of its side effects, mainly the photo-toxicity. In this paper fluorescence spectra in non-protic solvents and different polarities were carried out along with theoretical calculations. Preliminary potential surfaces of the keto and enol forms were obtained at AM1 level of theory providing the most stable conformers, which had their structure re-optimized through the B3LYP/CEP-31G(d,p) method. From the optimized structures, the electronic spectra were calculated using the TD-DFT method in vacuum and including the solvent effect through the PCM method and a single water molecule near PRX. A new potential surface was constructed to the enol tautomer at DFT level and the most stable conformers were submitted to the QST2 calculations. The experimental data showed that in apolar media, the solution fluorescence is raised. Based on conformational analysis for the two tautomers, keto and enol, the results indicated that the PRX-enol is the main tautomer related to the drug fluorescence, which is reinforced by the spectra results, as well as the interconvertion barrier obtained from the QST2 calculations. The results suggest that the PRX one of the enol conformers presents great possibility of involvement in the photo-toxicity mechanisms.     

Application of an optimization technique to the discretized version of the Griffin–Hill–Wheeler–Hartree–Fock equations

Application of the SIMPLEX optimization method to define the mesh of the discretized version of the Griffin–Hill–Wheeler–Hartree–Fock (GHWHF ) equations was studied. Improved discretization parameters with respect to the original method were obtained for atomic systems with two or four electrons and for the H₂ molecule. For the atomic systems, the following correlations between the discretization parameters and the total energy were found: N = a · In(ΔE) + b; Ω₀ = a′ · In(ΔΩ) + a″; and In(ΔΩ) = b′ · ln(N) + b″. These equations provide a systematic procedure to reach a desired degree of accuracy in the energy for the atomic systems studied as well as to fix the basis set to be employed. These equations are similar to those found earlier for eventempered basis sets and permit the establishment of a relationship between the two methods. The even-tempered method is also an approximate solution of the GHWHF equations. The optimized integral discretized basis is more efficient in representing small basis sets for atoms and the basis for the hydrogen molecule in comparison to the even-tempered one. The optimization procedure was successfully applied to generate the universal basis for the atomic systems studied.     

Electrospray ionization mass spectrometry fingerprinting of propolis

Crude ethanolic extracts of propolis, a natural resin, have been directly analysed using electrospray ionization mass (ESI-MS) and tandem mass spectrometry (ESI-MS/MS) in the negative ion mode. European, North American and African samples have been analyzed, but emphasis has been given to Brazilian propolis which displays diverse and region-dependent chemical composition. ESI-MS provides characteristic fingerprint mass spectra, with propolis samples being divided into well-defined groups directly related to their geographical origins. Chemometric multivariate analysis statistically demonstrates the reliability of the ESI-MS fingerprinting method for propolis. On-line ESI-MS/MS tandem mass spectrometry of characteristic [M - H](-) ion markers provides an additional dimension of fingerprinting selectivity, while structurally characterizing the ESI-MS marker components of propolis. By comparison with standards, eight such markers have been identified: para-coumaric acid, 3-methoxy-4-hydroxycinnamaldehyde, 2,2-dimethyl-6-carboxyethenyl-2H-1-benzopyran, 3-prenyl-4-hydroxycinnamic acid, chrysin, pinocembrin, 3,5-diprenyl-4-hydroxycinnamic acid and dicaffeoylquinic acid. The negative mode ESI-MS fingerprinting method is capable of discerning distinct composition patterns to typify, to screen the sample origin and to reveal characteristic details of the more polar and acidic chemical components of propolis samples from different regions of the world.     

The virial theorem as an entail for Koopmans' theorem in atomic calculations

The frozen approximation in the Koopmans' theorem suggests that the virial theorem is not obeyed. By imposing the virial theorem to Koopmans' theorem, we observe that the ionization potential of an atomic orbital is directly related to the respective kinetic energy and that the virial theorem introduces some reorganization effect on the electronic cloud. The quantity of reorganization introduced is not hazard, depending on the type of atom as well as the atomic orbital.